There are many applications which require electrical or thermal passageways through components. For instance, some electronic components require electrically isolated paths through the walls or base of a housing or substrate. These passageways are normally formed by casting a hole in a component and then connecting a feed-through, comprised of an electrical conductor inside an insulator, inside the hole. Typically, the insulator is either cemented, soldered or fused into the hole. For instance, with respect to fusing, a glass frit insert with a hole through the center can be placed into a hole in an electrical package. A pin is then placed in the hole of the glass frit. The whole system is then heated so that the glass melts and fuses to the metal of the package and the pin to form a hermetic electrically isolated electrical feed-through.
Another known method to produce feed-throughs is to produce glass-to-metal seals whereby a conductor pin is bonded to glass, such as borosilicate in a metal ring such as kovar. The metal ring with feed-throughs is then brazed or cemented into another part for providing electrical feed-throughs. Much development has occurred in this area and these types of feed-throughs are available from companies such as Balo Precision Parts, Inc. and Olin Aegis, Inc.
Another known method of producing electrical feed-throughs involves co-fired ceramics. In this method, a ceramic substrate is tape cast and an electrical conductive material is silk screened onto the ceramic, then another piece of ceramic is laid on top of the screened conductive material. The system is then fired to bond the ceramic pieces together with the conductive trace running through it. This type of feed-through is made by a number of companies including Coors Ceramics, Inc. and Sumatoma, Inc. To install this type of feed-through on a component, such as an electronic package, it can either be cemented in place or the outside of the feed-through can be selectively plated and then soldered into a metal package. This type of feed-through is normally made of approximately 95% to 98% dense alumina. However, the nature of this type of feed-through makes it difficult to produce so that it is hermetic. The resultant ceramic is not completely hermetic because it will allow a small amount of gas to flow through it.
Feed-throughs may also be made by use of a plastic, epoxy or other thermal set or thermal cure material in place of glass or ceramic. However, these type of feed-throughs have problems with higher temperatures because of melting and cracking which may occur, and they also absorb water and cause electronic problems.
The present invention describes a method, ideal but not limited, for making electrical feed-throughs which are hermetic and are not sensitive to heat. The present invention produces feed-throughs at low cost with a high number of vias that are hermetic. The present invention allows for the production of electronic components with in-situ feed-throughs with only minimal secondary operations. The present invention also allows for high quantities of closely spaced hermetic vias.